function gcpick_cmdhelp(cmd)
%cmdhelp - display command information
cmdset={'plot', ...
    'change', ...
    'pick', ...
    'save', ...
    'load', ...
    'help', ...
    'quit'};
infoset={'plot station\nplot wave', ...
    'change station', ...
    'pick -wave p/s\n     -polar E/N/Z', ...
    'save mat\nsave xlsx', ...
    'load sac\nload mat', ...
    'list help', ...
    'exit'};
if isempty(cmd)
    for i = 1:length(cmdset)
        fprintf('%s -- \n\t%s\n', cmdset{i}, infoset{i});
    end
end
loc = ismember(cmdset, cmd);
if loc==0
    disp('No such cmd');
else
    fprintf('%s -- \n\t%s\n', cmdset{loc}, infoset{loc});
end
end